CHAP. III.] CONSTITUTION OF TYROSINE. 247 



undissolved substance remained, whilst from the solution were 

 separated 42*o grammes of coagulated albumin and albuminate. 

 By subtracting the amount of the undissolved matter as well as the 

 mass of the coagulated albumin and albuminate from the total 

 quantity of water free fibrin and gland we obtain the amount 

 of the substances in solution (382 + 15'2) - (ll'O + 42'5) = 3437 

 grammes. Of these, 211 '2 grammes consisted of peptone, 13*3 

 grammes of tyrosine, and 31 '6 grammes of leucine. If we calculate 

 the percentage of tyrosin and leucine obtained, in terms of the water- 

 free proteid matter submitted to digestion (397'2 grammes), we find 

 that the yield of tyrosine amounted to 3'3, and of leucine to 7*9 

 per cent. We have stated (see p. 246) that by treating blood-fibrin by 

 the sulphuric acid method, Erlenmeyer and Schoffer obtained only 

 2 per cent, of tyrosine, though the yield of leucine was 14 per cent. 

 By his barium hydrate method, Schutzenberger obtained from 

 blood-fibrin 3*3 per cent, of its weight of tyrosine. From a com- 

 parison of the results, we must conclude that the yield of tyrosine 

 when blood-fibrin is subjected to the action of trypsin is larger than 

 it is by either sulphuric acid or the barium hydrate method. The 

 comparative smallness of the yield of leuciue as compared with 

 that of tyrosine probably depended upon the greater difficulty of 

 separating quantitatively the more soluble proximate principle. 



Constitution Tyrosine is an aromatic compound. On many 

 of tyrosine. grounds it has come to be generally looked upon as 

 derived from one of the three oxyphenylpropionic acids, viz. from 

 the one which is designated para or p-oxyphenylpropionic acid. 

 This relation will be rendered obvious by the following constitutional 

 and graphic formulae. 



1. Para-oxyphenyl-a-propionic acid. 



C-CH 2 -CH 2 -CO.OH 

 pOH 



C 6 H 4 ( CH 



X CH . CH 2 -COOH: 



C(OH) 



If we now replace an H, by NH 2 -, in a CH 2 in the side chain of 

 paroxyphenylpropionic acid, we obtain paroxyphenyl-a-amidopropionic 

 acid, i.e. tyrosiue, thus : 



C - CH 2 - CH(NH 2 ) - CO . OH 

 pOH /\ 



C 6 H 4 ( CH CH 



X CH 2 .CH(NH 2 ).COOH: 



CH CH 



C(OH) 



